As summarized in the Center Overview, abnormalities in the circuitry of the dorsolateral prefrontal cortex (DLPFC) in schizophrenia may be more prominent in layer 3 than in other cortical layers. For example, DLPFC layer 3 pyramidal neurons exhibit somatodendritic morphological abnormalities, and these changes may preferentially affect a subpopulation of pyramidal neurons in this laminar location (see Project 1-Lewis). In order to explore the molecular counterpart to the morphological alterations observed in layer 3, we propose to test the following three hypotheses: 1) DNA microarrays can uncover multiple expression alterations in DLPFC layer 3 of subjects with schizophrenia that are not evident when all layers are analyzed together; 2) Some expression differences observed in layer 3 of subjects with schizophrenia are specific for subpopulations of projection neurons; and 3) Molecular markers that show expression alterations in subjects with schizophrenia are present in pyramidal neurons that share a common projection target. These hypotheses, which are complementary to those proposed in Project 1-Lewis, will be assessed in the following three specific aims. In Aim 1, using high density cDNA microarrays, we will compare deep layer 3 transcriptomes to whole DLPFC harvests in control subjects. This will identify genes that show expression enrichment in DLPFC deep layer 3. Following this, using the same microarrays and laser dissection microscopy we will identify mRNA expression differences in DLPFC layer 3 between pairs of subjects with schizophrenia and matched controls. In Aim 2 we will determine the cellular localization of the most promising expression changes using in situ hybridization and identify markers that show altered transcript levels in a subpopulation of projections neurons. In Aim 3 we will determine whether the subpopulations of DLPFC pyramidal neurons affected in schizophrenia share common projection targets by combining retrograde tracing of monkey DLPFC neurons with in situ hybridization using markers validated in Aim 2. These investigations have a number of conceptual and technical links with other Center projects and depend upon support provided by all of the proposed cores.